In the past, for silver electroplating solutions, silver electroplating solutions using a cyanide as a silver source and including compounds of As, Tl, Se, and Te as brighteners have been known (Japanese Patent No. 2756300).
By adding these gloss agents, there are the advantages that glossy silver plating films are obtained even with slight amounts of addition, the brightness degree increases the greater the amount of addition, the working current density is raised, and the speed is increased.
On the other hand, when forming silver plating films at front ends of inner leads or die pads etc. of lead frames for semiconductor packages, if bright (meaning becoming close to mirror surfaces), conversely problems such as image recognition not being possible at the time of wire bonding and sealability becoming inferior arise. Consequently, plating aiming at matt or semi-bright has been performed. Therefore, it has been necessary to lower the amounts of addition of brighteners.
In the case of the above gloss agents, however, originally only very small amounts were added, so if further lowering the amounts of addition, analysis becomes difficult and routine control of the amounts of addition by analysis becomes impossible. In practice, the amounts of addition are judged by the experience and judgment of the workers. Good control over the amounts of addition is therefore difficult.
Further, if reducing the amounts of addition of gloss agents, the working current density becomes low and the range becomes narrower, the production efficiency drops, and plating defects easily occur. In this case, if raising the working current density to raise the production efficiency, so-called “burnt deposits” or uneven plating ends up occurring.